THE INTEGUMENTARY

SYSTEM
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THE INTEGUMENTARY SYSTEM

The integumentary system is the body's largest
organ system, which includes the skin, hair,
nails, and various glands.

The skin is the most visible part of the

integumentary system and serves as a barrier
against physical, chemical, and biological
factors. It regulates body temperature,
sensation, and protects against dehydration by
retaining fluids.

The hair and nails provide additional protection

to the skin, and the glands secrete sweat,
sebum, and other substances that aid in the
regulation of body temperature and other bodily
functions.
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THE SKIN
The skin is the largest organ of the body and is
composed of three layers: the epidermis, dermis, and
hypodermis.

1. Epidermis: This is the outermost layer of the skin,

which is made up of four to five layers of cells. It
contains no blood vessels, and its main function is
to protect the body from the external environment.
2. Dermis: This is the middle layer of the skin, which
contains connective tissue, blood vessels, and
nerves. It is responsible for providing strength and
flexibility to the skin and helps regulate body
temperature.
3. Hypodermis: This is the deepest layer of the skin,
which consists of adipose tissue and connective
tissue. Its main function is to attach the skin to
underlying bones and muscles, as well as to store
energy in the form of fat.
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THE EPIDERMIS
The epidermis is the outermost layer of the skin, and its primary function is to protect the underlying layers of the
skin from the external environment. It is composed of multiple layers of cells, including keratinocytes, melanocytes,
and Langerhans cells.

Keratinocytes are the most abundant cells in the epidermis and are responsible for producing the protein keratin,
which forms a protective barrier on the surface of the skin. Melanocytes are responsible for producing the pigment
melanin, which provides protection against the harmful effects of UV radiation. Langerhans cells are involved in the
immune response and help to identify and eliminate pathogens.

The epidermis is composed of four distinct layers, including the stratum basale, stratum spinosum, stratum
granulosum, and stratum corneum. The stratum basale is the deepest layer and contains stem cells that
continuously divide and differentiate into the other layers of the epidermis. The stratum spinosum is the thickest
layer and contains keratinocytes that produce the protein filaggrin, which helps to maintain the barrier function of the
skin. The stratum granulosum is a thin layer that contains keratinocytes that produce lipids, which help to prevent
water loss from the skin. The stratum corneum is the outermost layer of the epidermis and is composed of layers of
flattened, dead keratinocytes that are continuously shed from the surface of the skin.

The epidermis is also rich in nerve endings, including Merkel cells and Meissner's corpuscles, which are involved in
touch sensation, and free nerve endings, which detect pain and temperature changes. Blood vessels are not
present in the epidermis, but small blood vessels in the dermis supply nutrients and oxygen to the epidermal cells.
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THE DERMIS
The dermis is the second layer of the skin, located beneath the epidermis. It is made up of dense irregular
connective tissue and contains a variety of structures, including blood vessels, nerves, sweat glands, hair follicles,
and sebaceous glands.

The dermis is divided into two layers: the papillary layer and the reticular layer.

Papillary Layer: This is the outer layer of the dermis, and it is composed of loose connective tissue. It contains
finger-like projections called papillae, which extend into the epidermis. The papillae contain blood vessels that
supply the epidermis with nutrients and oxygen, as well as sensory receptors that detect touch, pressure, and
temperature.

Reticular Layer: This is the deeper and thicker layer of the dermis, composed of dense irregular connective tissue.
It contains collagen and elastic fibers, which provide strength and elasticity to the skin. The reticular layer also
contains blood vessels, nerves, sweat glands, hair follicles, and sebaceous glands.

The dermis also contains specialized cells called fibroblasts, which produce collagen and other proteins that give
the skin its strength and elasticity. Additionally, the dermis contains immune cells that help protect the body from
infection.
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THE HYPODERMIS
The hypodermis, also known as the subcutaneous tissue or superficial fascia, is the deepest layer of the skin.
It is composed of loose connective tissue and adipose tissue (fat cells) that connect the skin to underlying
bone and muscle.

The main functions of the hypodermis include insulation, protection, and energy storage. It provides thermal
insulation to the body by preventing heat loss and absorbing external shocks that may cause injury to the
underlying structures.

The hypodermis plays a role in energy storage by storing excess calories in the form of adipose tissue, which
can be used by the body for energy when needed. Adipose tissue also releases hormones that help regulate
metabolism, appetite, and other physiological processes.

Blood vessels and nerves that supply the skin and underlying structures pass through the hypodermis. The
blood vessels provide nutrients and oxygen to the skin and remove waste products, while the nerves transmit
signals from the skin to the brain and vice versa, enabling sensations such as touch, pressure, and pain.
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GLANDS
The integumentary system does not have glands in the traditional sense, but it includes specialized
structures that produce and secrete substances onto the skin's surface, such as:

• Sweat Glands: There are two types of sweat glands in the skin, eccrine and apocrine. Eccrine
glands are found all over the body and produce sweat that helps regulate body temperature.
Apocrine glands are found in the armpits and groin areas and produce a thicker, milky sweat that
can be broken down by bacteria, leading to body odor.
• Sebaceous Glands: These glands are found throughout the skin, except for the palms and
soles of the feet. They secrete an oily substance called sebum that helps keep the skin
moisturized and protects it from external factors like bacteria and fungi.
• Mammary Glands: These are specialized sweat glands that are found only in the breasts. They
produce milk for nursing infants.
• Ceruminous Glands: These are modified sweat glands that produce earwax or cerumen in the
ear canal. Earwax helps protect the ear from foreign particles and keeps the skin of the ear
canal lubricated.
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HAIR
Hair is a filamentous biomaterial that grows from the skin
of mammals. It is composed mainly of the protein
keratin, which is produced in specialized cells called hair
follicles that are located in the dermis layer of the skin.

Each hair follicle consists of a bulb, a root, and a shaft.

The bulb is the base of the follicle, and it contains the
living cells that produce the hair. The root is the portion
of the hair that is embedded in the skin, while the shaft is
the visible part of the hair that protrudes above the skin
surface.

The hair shaft is composed of three layers: the medulla,

cortex, and cuticle. The medulla is the innermost layer
and is composed of loosely packed cells. The cortex is
the middle layer and is composed of densely packed
cells that contain the pigment that gives hair its colour.
The cuticle is the outermost layer and consists of
overlapping scales that protect the cortex and medulla
from damage.
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HAIR
Hair growth occurs in cycles, with three phases:
anagen, catagen, and telogen. During the
anagen phase, which lasts from two to seven
years, the hair grows actively. In the catagen
phase, which lasts for a few weeks, the growth
of the hair slows down and the follicle shrinks.
Finally, in the telogen phase, which lasts for
several months, the hair stops growing and
eventually falls out, making way for new hair
growth.

Hair also has several specialized structures

associated with it, including sebaceous glands,
which produce sebum that helps to lubricate
and protect the hair and skin, and arrector pili
muscles, which are attached to the hair follicles
and contract in response to cold or emotional
stress, causing the hair to stand up (also known
as "goosebumps").
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NAILS
Nails are hard, flattened, translucent plates that
grow from the nail matrix, which is a specialized
structure located beneath the proximal end of the
nail. They are made up of layers of dead,
compacted, and hardened keratinized cells that are
pushed out and grow from the matrix.

The nail plate is the visible part of the nail that

covers the nail bed. It is composed of several layers
of compacted dead skin cells called keratinocytes.
The nail plate is translucent, allowing the pinkish
colour of the underlying nail bed to show through.

The nail bed is the layer of skin on which the nail

plate rests. It is highly vascular and gives the nail its
pink colour. The nail bed is responsible for
producing new nail cells that push the nail plate
forward as it grows.
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NAILS
The nail matrix is a specialized structure located
beneath the proximal end of the nail bed. It is
responsible for producing new nail cells that push
the nail plate forward as it grows. The matrix is
highly vascular and contains nerves and lymphatic
vessels.

The lunula is the half-moon-shaped area at the

base of the nail plate that is visible through the nail.
It is the most active area of the nail matrix and
contains the growing portion of the nail plate.

The cuticle is a thin layer of skin that covers the

base of the nail plate. It acts as a seal to protect the
nail matrix and the nail bed from infection.

The nail root is the portion of the nail that is

embedded in the skin at the base of the nail plate. It
is responsible for anchoring the nail to the
underlying tissue.
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